A prior art optical control is described in U.S. Pat. No. 4,859,965, issued Aug. 22, 1989. The prior art optical control includes a light source for emitting light at a selective wavelength, control means coupled to said light source for controlling the intensity of the light emitted from said source, a fixed resistance, a GaAs multi-finger FET having parallel connected sources and parallel connected drains and parallel connected gate fingers, circuit means for connecting the sources and drains of said FET in series circuit with said fixed resistance across a source of positive dc voltage, optic fiber means optically coupled from said light source on the surface of said FET between the sources and drains of the FET and covering substantially all of the gate fingers of the FET, gate biasing means coupled to the gates of said FET for biasing said FET to a point near pinch-off to maximize the light sensitivity of the FET, an output lead coupled to a circuit junction of said fixed resistance and said FET, whereby changes in the intensity of light from said light source change the voltage drop across said FET and change the output from the output conductor.
Related prior art publications include:
1. Buck, D. C., and M. A. Cross, "Optical Injection Locking of FET Oscillators Using Fiber Optics", IEEE MTTSymposium, Digest of Papers, 1986. PA0 2. Seeds, A. J., and A. A. De Salles, "Optical Control of Microwave Semiconductor Devices," IEEE Transactions on Microwave Theory and Techniques, Vol. 38, no. 5, May 1990. PA0 3. U.S. Pat. No. 5,073,718, issued to Paollela on Dec. 17, 1991, and entitled, "Optical Control of a Microwave Switch". PA0 4. U.S. Pat. No. 5,162,657 issued to Sturzebecher et al on Nov. 10, 1992 and entitled, "Optical Control of a Microwave Variable Attenuator." PA0 5. U.S. Pat. No. 5,144,261 issued to Harvey et al on Sep. 1, 1992 and entitled, "Optically Injection Locked Resonant Tunnel Diode Oscillator". PA0 6. U.S. Pat. No. 5,373,261 issued to Higgins et al on Dec. 13, 1994 and entitled, "An Improved Direct Optical Injection Locked FET Oscillator."
The references show that the technology of microwave light generation and delivery using lasers, light emitting diodes, plasma tubes and the like in combination with intensity modulators and fiber optics is well known. Therefore, as is suggested by the above identified references, one skilled in the art would readily be able to design any number of optical or integrated optic systems to deliver light intensity modulated at microwave or millimeter wave frequencies to the semiconductive device and incorporate such a semiconductive device in oscillator circuit applications.
An example of important technical fields where such semiconductor devices would be able to be directly incorporated in phased array radar and communication systems and in remote antenna systems. As suggested by the above references, intensity modulated light would modulate active oscillator modules using these semiconductor devices and can be distributed over an antenna array remote from the rest of the radar or communication system. One means of achieving modulation, is by modulating oscillators with a direct optical signal delivered over optical fibers. Various means are available to optically control semiconductor devices, including the direct optical modulation of oscillators utilizing IMPATT and Gunn diodes. However, these semiconductor devices are difficult to integrate into MMIC systems, and lack some of the enhanced performance characteristics of a MESFET field effect transistor and, therefore, integration and locking of oscillator modules in MMIC (microwave monolithic integrated circuit) systems would be further optimized by optically controlling MESFETS incorporated in such oscillators.
The present invention addresses this present need for direct optical control of a MESFET to modulate or lock a MESFET oscillator.